Converter and power conversion device using same

Abstract

A converter includes a first diode having an anode and a cathode connected respectively to an input terminal and a first output terminal, a second diode having an anode and a cathode connected respectively to a second output terminal and the input terminal, a first transistor connected between the first output terminal and the input terminal, a second transistor connected between the input terminal and the second output terminal, and a bidirectional switch connected between the input terminal and a third output terminal and including third to sixth diodes and a third transistor. Each of the first diode, the second diode, and the third transistor is made of a wide bandgap semiconductor. Each of the first and second transistors and the third to sixth diodes is made of a semiconductor other than the wide bandgap semiconductor.

The invention claimed is: 
     
       1. A converter that converts an AC voltage supplied to an input terminal into first to third DC voltages and outputs the first to third DC voltages respectively to first to third output terminals, the converter comprising:
 a first diode having an anode and a cathode connected respectively to the input terminal and the first output terminal; 
 a second diode having an anode and a cathode connected respectively to the second output terminal and the input terminal; 
 a first transistor connected between the first output terminal and the input terminal; 
 a second transistor connected between the input terminal and the second output terminal; and 
 a first bidirectional switch connected between the input terminal and the third output terminal, 
 the first DC voltage being higher than the second DC voltage, and the third DC voltage being an intermediate voltage between the first and second DC voltages, 
 the first bidirectional switch including third to sixth diodes and a third transistor, 
 the third and fourth diodes having anodes connected respectively to the input terminal and the third output terminal and cathodes connected together to a first electrode of the third transistor, 
 the fifth and sixth diodes having cathodes connected respectively to the input terminal and the third output terminal and anodes connected together to a second electrode of the third transistor, 
 each of the first diode, the second diode, and the third transistor being made of a wide bandgap semiconductor, 
 each of the first transistor, the second transistor, and the third to sixth diodes being made of a semiconductor other than the wide bandgap semiconductor, 
 wherein a rated current of each of the first and second diodes is greater than a rated current of each of the third to sixth diodes and the first to third transistors. 
 
     
     
       2. The converter according to  claim 1 , wherein
 the first and third transistors are alternately turned on when the AC voltage is a positive voltage, and
 the second and third transistors are alternately turned on when the AC voltage is a negative voltage. 
 
 
     
     
       3. The converter according to  claim 1 , comprising a semiconductor module including the first to sixth diodes and the first to third transistors. 
     
     
       4. The converter according to  claim 1 , wherein a rated current of each of the first and second transistors is smaller than the rated current of each of the first to sixth diodes and the third transistor. 
     
     
       5. The converter according to  claim 1 , wherein the wide bandgap semiconductor comprises SiC, and the semiconductor other than the wide bandgap semiconductor comprises Si. 
     
     
       6. A power conversion apparatus comprising:
 a converter according to  claim 1 ; and 
 an inverter configured to convert first to third DC voltages supplied respectively to the first to third output terminals into an AC voltage at three levels and output the AC voltage to a fourth output terminal, 
 the inverter including
 a fourth transistor having first and second electrodes connected respectively to the first and fourth output terminals, 
 a fifth transistor having first and second electrodes connected respectively to the fourth and second output terminals, 
 seventh and eighth diodes connected respectively in anti-parallel with the fourth and fifth transistors, and 
 a second bidirectional switch connected between the third and fourth output terminals, 
 
 the second bidirectional switch including sixth and seventh transistors and ninth and tenth diodes, 
 each of the fourth transistor, the fifth transistor, the ninth diode, and the tenth diode is made of the wide bandgap semiconductor, and 
 each of the sixth transistor, the seventh transistor, the seventh diode, and the eighth diode is made of a semiconductor other than the wide bandgap semiconductor. 
 
     
     
       7. The power conversion apparatus according to  claim 6 , wherein
 the sixth and seventh transistors have first electrodes connected to each other and second electrodes connected respectively to the third and fourth output terminals, 
 the ninth and tenth diodes are connected respectively in anti-parallel with the sixth and seventh transistors, 
 the seventh transistor is turned on and the fourth and sixth transistors are alternately turned on when the first and third DC voltages are alternately output to the fourth output terminal, and 
 the sixth transistor is turned on and the fifth and seventh transistors are alternately turned on when the second and third DC voltages are alternately output to the fourth output terminal. 
 
     
     
       8. The power conversion apparatus according to  claim 6 , wherein
 the sixth and seventh transistors have first electrodes connected respectively to the fourth and third output terminals and second electrodes connected to each other, 
 the ninth and tenth diodes are connected respectively in anti-parallel with the sixth and seventh transistors, 
 the seventh transistor is turned on and the fourth and sixth transistors are alternately turned on when the first and third DC voltages are alternately output to the fourth output terminal, and 
 the sixth transistor is turned on and the fifth and seventh transistors are alternately turned on when the second and third DC voltages are alternately output to the fourth output terminal. 
 
     
     
       9. The power conversion apparatus according to  claim 6 , wherein
 the sixth and seventh transistors have second electrodes connected respectively to the third and fourth output terminals, 
 the ninth and tenth diodes have anodes connected respectively to the third and fourth output terminals and cathodes connected respectively to first electrodes of the seventh and sixth transistors, 
 the seventh transistor is turned on and the fourth and sixth transistors are alternately turned on when the first and third DC voltages are alternately output to the fourth output terminal, and 
 the sixth transistor is turned on and the fifth and seventh transistors are alternately turned on when the second and third DC voltages are alternately output to the fourth output terminal. 
 
     
     
       10. The power conversion apparatus according to  claim 6 , wherein the inverter includes a semiconductor module including the fourth to seventh transistors and the seventh to tenth diodes. 
     
     
       11. The power conversion apparatus according to  claim 6 , wherein a rated current of each of the fourth and fifth transistors is greater than a rated current of each of the sixth and seventh transistors and the seventh to tenth diodes. 
     
     
       12. The power conversion apparatus according to  claim 6 , wherein the wide bandgap semiconductor comprises SiC, and the semiconductor other than the wide bandgap semiconductor comprises Si.